Method for rendering cathode-ray tube more resistant to implosion and product thereof

ABSTRACT

The inner surface of a reinforcing structure adapted to encircle a faceplate panel of the tube is provided with a nontacky coating of a tackifiable, adhesive material. When the tube is ready for reinforcing, the coating is made tacky, as by applying thereto an organic solvent. The reinforcing structure is positioned around the panel with the tacky coating against the panel. Then, with the structure in place, the tackiness is removed from the coating.

llited States Patent n91 Platt [451 Nov. 5, 1974 METHOD FOR RENDERING CATHODE-RAY TUBE MORE RESISTANT T0 llMlPLOSlON AND PRODUCT THEREOF [75] Inventor: Richard Bibby Platt, Midland,

Ontario, Canada [73] Assignee: RCA Corporation, New York, NY.

[22] Filed: Oct. 10, 1972 [21] Appl. No.: 295,853

[52] US. Cl. 29/25.l3, 117/122 S, 117/132 CB, 156/307, 156/309, 156/334, 161/147,

[51] Int. Cl 1101] 9/18, l-lOlj 29/06, C09j 5/00 [58] Field of Search 117/122 S, 132 CB; 156/307, 309, 334; 161/147, 203; 178/7.82;

[5 6] References Cited UNITED STATES PATENTS 2,348,447 5/1944 Bock 260/328 Palmquist et al. 161/214 3,456,076 7/1969 Griswold et al 178/7.82 3,508,310 4/1970 Eisses 29/25.13 3,513,056 5/1970 Middlebrook 156/309 3,553,051 1/1971 Warrach et al... 156/309 3,708,369 1/1973 Bongenaar et 211.... 156/322 Primary ExaminerCharles E. Van Horn Assistant ExaminerRobert A. Dawson Attorney, Agent, or FirmG. H. Bruestlc; L. Greenspan [57] ABSTRACT The inner surface of a reinforcing structure adapted to encircle a faceplate panel of the tube is provided with a nontacky coating of a tackifiable, adhesive material. When the tube is ready for reinforcing, the coating is made tacky, as by applying thereto an organic solvent. The reinforcing structure is positioned around the panel with the tacky coating against the panel. Then, with the structure in place, the tackiness is removed from the coating.

4 Claims, 3 Drawing Figures METHOD FOR RENDERING CATHODE-RAY TUBE MORE RESISTANT TO IMPLOSION AND PRODUCT THEREOF BACKGROUND OF THE INVENTION This invention relates to a novel method for rendering a cathode-ray tube more resistant to implosion, and to a novel cathode-ray tube made by the novel method.

One form of a cathode-ray tube comprises an evacuated envelope including a glass faceplate panel having a rearwardly-extending flange or sidewall. Atmospheric pressure pressing against the external surface of the panel may exert forces totaling several tons against the faceplate. Should the faceplate panel shatter (implode), these forces will drive fragments into the tube, which fragments may bounce back out or continue through the shattered panel and cause injury to persons nearby.

It has been proposed to render a cathode-ray tube more resistant to implosion by encircling the faceplate panel with a metal or plastic reinforcing structure which will hold the flange or sidewall thereof in place should a fracture occur. In some forms, the reinforcing structure is attached to the tube with an adhesive, and may or may not include a tensioned metal band encircling the panel.

In one prior process of assembly, controlled amounts -of adhesive are applied to parts of the reinforcing structure; then, while the adhesive is still wet, the parts are positioned on the tube. In another prior process, the parts of the reinforcing structure are assembled on the tube, and then controlled amounts of adhesive are injected between the tube and the reinforcing structure. In either case, the adhesive application and the mounting of the metal parts to the picture tube are required to be carried out on a concurrent basis. Moreover, the nature of theadhesive that is employed results in a certain amount of the adhesive being exuded onto the picture tube from which it must be cleaned by hand, an operation that requires additional labor.

SUMMARY OF THE INVENTION The novel method for rendering a cathode-ray tube more resistant to implosion comprises providing a reinforcing structure adapted to encircle the tube. The inner surface of the reinforcing structure carries a nontacky coating of an adhesive material that can be made tacky; that is, tackifiable. When the tube is ready for reinforcement, the coating is made tacky. Then, with the coating tacky, the reinforcing structure is positioned around the tube with the tacky coating against the tube. The tackiness is removed from the coating so as to adhere the structure to the tube.

By providing a reinforcing structure with a dry, nontacky, preapplied, tackifiable adhesive coating, many advantages may-be realized. The adhesive application process may be separated in time and space from the assembly step. There is more economical use of adhesive and less chance of exudation and flowing of the adhesive that would require cleaning.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a novel cathode-ray tube of the invention.

2 FIG. 2 is an enlarged fragmentary vertical sectional view of a portion of the tube of FIG. 1 taken along line 2-2.

FIG. 3 is an exploded view illustrating the individual components used to make the tube shown in FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the preferred embodiment, illustrated in FIGS. 1 and 2, a cathode-ray tube 10 is shown, which includes an evacuated envelope 11. The envelope 11 comprises a faceplate panel 12, a neck 14 and an interconnecting funnel 15. The neck 14 is closed at its distal end with a stem 17. An electron gun (not shown) is housed within the neck 14 and connects to base prongs 18, which are supported by and extend externally from the stem 17. The neck 14 is sealed to and closes the small end of the funnel 15.

The faceplate panel 12 includes a glass viewing window 19 and an integral, rearwardly extending glass sidewall or flange 20 extending continuously around the window 19. The panel 12 closes and is sealed to the wide end of the funnel 15 along the seal line 21 at the terminal end of the flange 20. A luminescent screen 22 is located on the interior surface of the viewing window 19.

The interior of the envelope is evacuated to a high level of vacuum of the order of 10' mm of mercury. In this example, with a 19V rectangular color picture tube, atmospheric pressure pressing against the external surface of the viewing window exerts forces totaling about 2 tons. Circumferential tensile stresses as high as 1,000 pounds per square inch are present in the flange 20 and the adjacent portion of the funnel.

A metal reinforcing structure 23 encircles the panel 12 around the outside of the flange 20 between the seal line 21 and the window 19. The reinforcing structure 23 includes two semiencircling metal rim plates 25 and 26, which are attached to the flange 20 with rubberbased adhesive 27. A continuous metal band 28 lays on top of the rim plates 25 and 26 between the mold match line 24 and the window 19. The band 28 is in tension with the ends thereof overlapped and crimped with a clip member 29. The rim plates 25 and 26 are contoured to the shape of the panel 12 to require a minimum thickness of adhesive 27 and to provide a firm foundation for the forces produced by the tensioned band 28. 7

The preferred example shown in FIGS. 1 and 2 may be assembled by the following procedure with reference to FIG. 3. There is provided a complete and operable l9V color television picture tube 10. There is also provided a metal band 28 and two U-shaped rim plates 25 and 26, which are each contoured and sized to fit on and semi-encircle thepanel 12 of the tube. The metal band is carbon-steel strapping about 0.75-inch wide and about 0.020-inch thick.

The rim plates 25 and 26 are each made of cold-roll steel that has been stamped to shape. The inner surfaces (those intended to face the panel) of the rim plates 25 and 26 are coated with a rubber-based adhesive that has been dried sufficiently to remove any tackiness. One suitable adhesive consists of two parts Weldwood Contact Cement marketed by Weldwood of Canada, Limited, Toronto, Ontario, and one part asbestos fines (through mesh). The adhesive is extruded through a flattened nozzle onto the surfaces of the rim plates 25 and 26 to a width of about 0.60 inch and then dried in air. As shown in FIG. 2, the adhesive coating 27 is located back of the bend or brow 30 of the rim plate 25. The adhesive coating 27 is about one-halfinch wide at its narrowest point in the corners of the rim plates, and about 1% inch wide at its widest point at about the middle of the rim plates.

When the tube is ready to be reinforced, the dry adhesive coatings 27 are wetted with toluene, which is quickly absorbed by the coatings, and the coatings become tacky again. The rim plates 25 and 26 are then pressed into position against the panel 12 of the tube 10. The adhesive 27 may be squeezed outwardly into the open volume between the rim plate 25 and the sidewall 20 shown in FIG. 2, but does not ooze beyond the rim plate 25. The metal band 28 is wrapped around rim plates 25 and 26, tensioned and then crimped with a clip member 29. The metal band may be positioned and crimped by the method described in US. Pat. No. 3,220,593 to D. E. Powell et al. Alternatively, the metal band may be positioned and welded by the method described in US. Pat. No. 3,162,933 to Alan M. Trax et al. The metal band 28 holds the rim plates 25 and 26 in place while the toluene evaporates from the adhesive 27, thereby removing the tackiness from the adhesive and producing a bond between the glass and the metal.

The tube thus produced will not implode when the panel 12 is fractured, as with a blow of foot-pounds. If the panel 12 fractures, air will rush in to replace the vacuum of the tube, but the envelope 11 will not collapse and glass fragments will not be thrown forward, as toward a viewer.

GENERAL CONSIDERATIONS AND ALTERNATIVES The invention may be applied to any cathode-ray tube which it is desirable or necessary to reinforce in order to improve its resistance to implosion. Thus, the reinforced tube may be an oscilloscope or a display tube, for example. The reinforced tube finds its greatest use as a color television picture tube. The tube is provided in its completed and operable form ready to receive the reinforcing structure.

The reinforcing structure may be in any form or arrangement known in the prior art in which a panelencircling structure is adhered to the panel. Such structures are disclosed, for example, in US. Pat. Nos. 3,220,593 to D. E. Powell et al. and 3,626,093 to James Inglis. In these prior patents, the adhesive is an epoxy resin or other self-setting resin which cannot be retackified. Such adhesives require that the reinforcing structure be installed on the tube before the adhesive has set.

The adhesive of the present method and tube is typically comprised of a rubber-based cement and a filler, which may be dried to nontackiness and then retackified by applying thereto an organic solvent for the cement. Rubberbased cements are known in the art. They are predominantly butadiene-styrene copolymers or neoprene polymers. Reclaimed rubber is a common ingredient of such cements. Rubber-based cement is sold as a tacky paste which contains one or more liquid solvents, such as toluene, trichloroethylene, and methyl chloroform. The adhesive may also contain one or more fillers. Preferred fillers are asbestos shorts, fines or flour. Calcium carbonate and talc may also be used. The filler is present in amounts between 0 and percent of the adhesive. The filler imparts increased viscosity to the adhesive, enabling it to be applied in greater thickness than unfilled adhesive.

The adhesive may be coated on the inner surfaces of the reinforcing structure by any convenient method. For example, the adhesive may be brushed on or sprayed on. For production situations, it is preferred to dispense the adhesive from a cartridge fitted with a suitably designed nozzle by low pressure directly onto the surfaces. The preferred viscosity of the adhesive is determined by trial. A few trials will easily show the viscosity at which the adhesive can be applied without undue spreading over the surface. The adhesive coating may be applied to the entire width of the inner surfaces of the reinforcing structure. However, it is preferred to apply a continuous strip that is less than the full width of the reinforcing structure so that any excess adhesive will remain under the reinforcing structure.

The adhesive coating dries in air in about 15 minutes to the point where the surface is no longer tacky and the part may be handled at will. When the tube is ready to receive the part, the coating is wetted with an organic solvent, such as the ones mentioned above, to retackify the coating. When the coating has become tacky, the part is pressed into place and held there, at least until the coating has dried to a nontacky condition and a bond develops between the envelope and the reinforcing structure.

The invention confers the following advantages:

1. It enables the adhesive application process to be divorced from the process of applying the reinforcing structure to the tube, thus permitting greater flexibility in the overall process.

2. The dried and retackified adhesive by its nature has little or no propensity to flow. Hence, there is no exudation of resin requiring a subsequent cleaning process.

3. As compared with epoxy-type cements, the rubber-based cements are relatively nonallergenic to factory workers.

4. The novel method requires relatively low-cost adhesives compared to systems employing epoxy-type cements.

5. As compared with coating a rubber-based adhesive to the reinforcing structure just prior to installation, the novel method of precoating and retackifying employs less solvent in the last step of the process.

I claim:

1. A method for rendering a cathode-ray tube more resistant to implosion, said tube comprising an evacuated envelope including a glass faceplate panel, said method comprising a. providing a reinforcing structure including two metal rim plates contoured to encircle said panel, the inner surface of said rim plates carrying a nontacky coating of an adhesive material that can be made tacky by applying thereto an organic solvent therefor,

b. tackifying said coating by applying thereto a controlled amount of an organic solvent therefor,

c. positioning said reinforcing structure around said panel with said tacky coating against the outer surface thereof,

d. positioning a metal band around said rim plates and said panel,

sive is selected from the class consisting of butadienestyrenecopolymers and neoprene polymers.

4. The method defined in claim 1 wherein said organic solvent is selected from the group consisting of toluene, trichloroethylene, and methyl chloroform. 

1. A METHOD FOR RENDERING A CATHODE-RAY TUBE MORE RESISTANT TO IMPLOSION, SAID TUBE COMPRISING AN EVACUATED ENVELOPE INCLUDING A GLASS FACEPLATE PANEL, SAID METHOD COMPRISING A. PROVIDING A REINFORCING STRUCTURE INCLUDING TWO METAL RIM PLATES CONTOURED TO ENCIRCLE SAID PANEL, THE INNER SURFACE OF SAID RIN PLATES CARRYING A NONTACKY COATING OF AN ADHESIVE MATERIAL THAT CAN BE MADE TACKY BY APPLYING THERETO AN ORGANIC SOLVENT THEREFOR, B. TACKIFYING SAID COATING BY APPLYING THERETO A CONTROLLED AMOUNT OF AN ORGANIC SOLVENT THEREFOR, C. POSITIONING SAID REINFORCING STRUCTURE AROUND SAID PANEL WITH SAID TACKY COATING AGAINST THE OUTER SURFACE THEREOF, D. POSITIONING A METAL BAND AROUND SAID RIM PLATES AND SAID PANEL, E. FIXING SAID POSITIONED BAND TO ITSELF. F. AND THEN DRYING SAID COATING TO ADHERE SAID REINFORCING STRUCTURE TO SAID PANEL.
 2. The method defined in claim 1 wherein said adhesive is an organic, polymeric rubber-based material.
 3. The method defined in claim 2 wherein said adhesive is selected from the class consisting of butadienestyrene copolymers and neoprene polymers.
 4. The method defined in claim 1 wherein said organic solvent is selected from the group consisting of toluene, trichloroethylene, and methyl chloroform. 